i believe the 970's are cheaper then the 960, so id say yes they are worth it, if were comparing apples to apples.
If your asking is a NVMe 970 is worth it over a SATA 950, then again, id say yes its worth it, NVMe's are vastly superior.
If your asking is a NVMe 970 is worth it over a Intel 660p, then no... unless you love running synthetic benchmarks all day long, you won't notice the difference in speed, however your wallet will notice the difference in price.